1. Field of the Invention
This invention relates to a double facer installed in a corrugating machine which bonds a single-faced corrugated fiberboard sheet and a liner together so as to manufacture a corrugated paper.
2. Description of Related Art
Conventionally known is a corrugating machine (apparatus for making corrugated fiberboard sheet) which bonds a single-faced corrugated fiberboard sheet and a liner together to make a corrugated paper (i.e., double-faced corrugated fiberboard sheet, double wall corrugated fiberboard sheet, triple wall corrugated fiberboard sheet, or multi wall corrugated fiberboard sheet formed by a larger number of layers; hereinafter referred to as corrugated fiberboard sheet).
Such a corrugating machine is constituted by a single facer, a double facer, a slitter scorer, a cutoff, a stacker, and the like. The single facer forms a single-faced corrugated fiberboard sheet, the double facer bonds the single-faced corrugated fiberboard sheet and a liner together to form a corrugated fiberboard sheet, and then thus formed corrugated fiberboard sheet is cut by the slitter scorer and cutoff into divided-plate-like corrugated fiberboard sheets, which are piled up in the stacker.
The double facer installed in such a corrugating machine will further be explained. FIG. 9 is a schematic side view showing an overall configuration of the double facer installed in the corrugating machine.
As shown in the schematic side view of FIG. 9, a double facer 100 installed in the corrugating machine bonds together a single-faced corrugated fiberboard sheet 1, which has been formed by a non-depicted single facer disposed upstream the double facer 100 (on the left side of FIG. 9) and whose flute leading edge has been provided with a glue at a glue machine 102, and a liner (bottom liner) 3, which has been conveyed from a non-depicted mill roll stand, thereby forming a corrugated fiberboard sheet 4. Here, depicted in FIG. 9 is the double facer 100 for forming a double-faced corrugated fiberboard sheet as the corrugated fiberboard sheet.
To this end, as shown in FIG. 9, the double facer 100 comprises a hot plate (heating box) 105 for heating the single-faced corrugated fiberboard sheet 1 and the liner 3 and causing the glue to gel and dry; an upper conveyor belt 106 for conveying the single-faced corrugated fiberboard sheet 1 and the liner 3; a plurality of press rolls 110 for pressing the single-faced corrugated fiberboard sheet 1 and the liner 3; and a lower conveyor belt 111 for conveying the single-faced corrugated fiberboard sheet 1 and liner 3 (yielding the double-faced corrugated fiberboard sheet 4 after being bonded together) while holding them between the upper conveyor belt 106 and the lower conveyor belt 111; thereby heating the single-faced corrugated fiberboard sheet 1 and the liner 3 while pressing them, and bonding them together to form the corrugated fiberboard sheet 4.
Here, the hot plate 105 is constituted by a plate-like member which is appropriately heated by steam, and is disposed at a lower part on the upstream side of the double facer 100.
The upper conveyor belt 106 is wound around two drums 107 and 108, while the drum 107 is driven by a non-depicted driving unit, whereby the upper conveyor belt 106 is driven to rotate. The upper conveyor belt 106 is provided with a belt-stretching unit 109 constituted by two rollers, thus yielding an appropriate tension.
The upper conveyor belt 106 is disposed at the upper part of the double facer 100 so as to convey the single-faced corrugated fiberboard sheet 1 and liner 3 (yielding the corrugated fiberboard sheet 4 after being bonded together) while holding them between the hot plate 105 and the lower conveyor belt 111, which will be explained later in detail.
Also, as shown in the schematic side view of FIG. 9, the press rolls 110 are used for yielding a pressing force required for bonding the single-faced corrugated fiberboard sheet 1 and the liner 3 together, and are arranged in series with each other along the sheet conveying direction, while each of which is constituted as a rodlike member extending over the widthwise direction of the corrugated fiberboard sheet 4. These press rolls 110 press the back face of the upper conveyor belt 106, thereby pressing the single-faced corrugated fiberboard sheet 1 and the liner 3 against the hot plate 105 disposed thereunder.
The lower conveyor belt 111 is disposed at a lower part on the downstream side of the upper conveyor belt 106, and conveys the corrugated fiberboard sheet 4 while holding it between the upper conveyor belt 106 and lower conveyor belt 111. In this case, a conveying force greater than the friction resistance occurring between the corrugated fiberboard sheet 4 and the hot plate 105 acts on the corrugated fiberboard sheet 4, whereby the corrugated fiberboard sheet 4 is pulled downstream.
As a result of such a configuration, the double facer 100 of the corrugating machine operates as follows.
Namely, the single-faced corrugated fiberboard sheet 1 formed by the non-depicted single facer is provided with a glue at its flute leading edge by the glue machine 102, and then is fed into the space between the hot plate 105, which is appropriately heated by steam, and the upper conveyor belt 106.
Then, both of the single-faced corrugated fiberboard sheet 1 and liner 3, in a laminated state, are conveyed as being held between the upper conveyor belt 106 and hot plate 105. Here, with an appropriate pressing force being applied thereto from the press rolls 110, the single-faced corrugated fiberboard sheet 1 and the liner 3 are bonded together as being heated by the hot plate 105, whereby the corrugated fiberboard sheet 4 is formed.
Thus formed corrugated fiberboard sheet 4 is conveyed as being held between the upper conveyor belt 106 and lower conveyor belt 111. Here, the bonding state between the single-faced corrugated fiberboard sheet 1 and the liner 3 is further secured, while their distortion, warping, and the like upon cooling are corrected.
In the above-mentioned conventional double facer 100, however, the upper conveyor belt 106 is disposed over substantially the whole region so as to oppose the hot plate 105, whereby the upper conveyor belt 106 and hot plate 105 always come into contact with the single-faced corrugated fiberboard sheet 1 and the liner 3. Consequently, there may be the following disadvantages.
Namely, in the process of heating the single-faced corrugated fiberboard sheet 1 and the liner 3 by the hot plate 105 and causing the glue to gel and dry, thereby bonding the single-faced corrugated fiberboard sheet 1 and the liner 3 together, moisture is released as the single-faced corrugated fiberboard sheet 1 and the liner 3 are heated. Consequently, the upper conveyor belt 106 absorbs thus released moisture at its portion in contact with the single-faced corrugated fiberboard sheet 1 and the liner 3, while releasing thus absorbed moisture at its portion not in contact with the single-faced corrugated fiberboard sheet 1 and liner 3. When moisture is absorbed and released by the upper conveyor belt 106, it influences the drying state of the glue applied between the single-faced corrugated fiberboard sheet 1 and the liner 3; and, according to circumstances, causes warping and the like in the corrugated fiberboard sheet 4, thereby deteriorating the quality of the latter.
Also, when the upper conveyor belt 106 is used for a long period of time, due to the above-mentioned absorption, release, and the like of moisture, it may lopsidedly wear out, or the glue and the like may adhere thereto, thereby forming irregularities on the belt surface. In this case, not only the conveyance of the upper conveyor belt 106 is influenced, but also the glue applied between the single-faced corrugated fiberboard sheet 1 and the liner 3 fails to attain a uniform drying state, thereby generating warping or the like in the corrugated fiberboard sheet 4 and deteriorating the quality thereof.
From such a viewpoint, it is preferable to do away with the upper conveyor belt 106. However, shortcomings may occur when the upper conveyor belt 106 is not provided. Namely, at the beginning of an operation in particular, i.e., when the single-faced corrugated fiberboard sheet 1 and the liner 3 are initially introduced into the machine, an operator must manually draw a tip of the single-faced corrugated fiberboard sheet 1 and the liner 3 so as to make them travel over the hot plate 105, thereby necessitating a large amount of time for preparation. This operation itself is difficult for the operator as well.
Meanwhile, the upper conveyor belt 106 of the double facer 100 functions to apply a conveying force to the single-faced corrugated fiberboard sheet 1 and liner 3 (yielding the corrugated fiberboard sheet 4 after being bonded together) and disperse the pressing force of the press rolls 110 so that it does not concentrate on one part.
Therefore, when the press rolls 110 each constituted as the rod-like member directly press the single-faced corrugated fiberboard sheet 1 and the liner 3, a local load may act on its contacting part with the single-faced corrugated fiberboard sheet 1, thereby collapsing the single-faced corrugated fiberboard sheet 1 and the liner 3.
On the other hand, the heat of the hot plate 105 constituting the double facer 100 is taken away by the single-faced corrugated fiberboard sheet 1 and liner 3 from thereabove, whereby the upper side of the hot plate 105 has a temperature lower than that on the lower side, thus generating thermal distortion between the upper and lower sides of the hot plate 105.
Also, how the heat is taken away from the hot plate 105 varies depending on the operation condition of the machine (e.g., conveying speed, width of the single-faced corrugated fiberboard sheet 1 and liner 3, and so on), thermal distortion may also occur on the upper surface of the hot plate 105 with a variable quantity.
Consequently, it has been difficult for the conventional press rolls 110 having a high flexural rigidity to apply an appropriate pressing force over the whole width of the single-faced corrugated fiberboard sheet 1 and liner 3 constantly and uniformly.
Also, depending on deviations of the thermal distortion and pressing force in the widthwise direction, the conventional press rolls 110 may fail to apply the pressing force uniformly over the whole surface of the single-faced corrugated fiberboard sheet 1 and liner 3, thus making it difficult to attain a favorable bonding state and improve the quality of the corrugated fiberboard sheet 4.